Check if an APK is from Google Play

With this method you can check if an APK was installed from Google Play

private boolean isFromGooglePlay(String pName) {
    PackageManager packageManager = this.getPackageManager();
    String installPM = packageManager.getInstallerPackageName(pName);
    if ( installPM == null ) {
        // Definitely not from Google Play
        return false;
    } else if ( installPM.equals("com.google.android.feedback") ) {
        // Installed from the Google Play
        return true;
    }
    return false;
}

More information: http://androidcracking.blogspot.com.es/2011/01/anti-cracking-example.html